Recording medium and dispersion of alumina hydrate

ABSTRACT

Disclosed herein is a recording medium comprising an alumina hydrate having an average pore radius of 20 to 200 Å and a half breadth of pore radius distribution of 20 to 150 Å.

This application is a continuation of application Ser. No. 08/462,961filed Jun. 5, 1995, now abandoned, which is a divisional of applicationSer. No. 08/231,659 filed Apr. 25, 1994 now U.S. Pat. No. 5,635,291.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a recording medium suitable for use inrecording using water-based inks, ink-jet recording method and adispersion. In Particular, this invention relates to a recording mediumwhich can provide images high in optical density, bright in color toneand high in resolution, and has excellent ink-absorbing capacity, anink-jet recording method using such a recording medium, and a dispersionof an alumina hydrate, which is suitable for use in production of therecording medium.

2. Related Background Art

In recent years, an ink-jet recording system, in which minute dropletsof an ink are flown by any of various working principles to apply themto a recording medium such as paper, thereby conducting recording ofimages, characters and/or the like, has been quickly spread as arecording apparatus for various images in various applications includinginformation instruments because it has features that recording can beconducted at high speed and with a low noise, color images can be formedwith ease, recording patterns are very flexible, and development andfixing process are unnecessary. Further, it begins to be applied to afield of recording of full-color images because images formed by anmulti-color ink-jet recording system are comparable in quality withmulti-color prints by a plate making system and photoprints by a colorphotographic system, and such records can be obtained at lower cost thanthe usual multi-color prints and photoprints when the number of copiesis small. With the improvement in recordability, such as speeding up andhigh definition of recording, and multi-coloring of images, recordingapparatus and recording methods have been improved, and recording mediahave also been required to have higher properties.

In order to satisfy such requirements, a wide variety of recording mediahave been proposed. For example, Japanese Patent Application Laid-OpenNo. 52-53012 discloses paper for ink-jet, in which a base paper web lowin sizing degree is impregnated with a surface coating. Japanese PatentApplication Laid-Open No. 53-49113 discloses paper for ink-jet, in whicha sheet containing urea-formalin resin powder therein is impregnatedwith a water-soluble polymer. Japanese Patent Application Laid-Open No.55-5830 discloses paper for ink-jet recording, in which a coating layerhaving good ink absorptiveness is provided on a surface of a base.Japanese Patent Application Laid-Open No. 55-51583 discloses thatamorphous silica is used as a pigment in a coating layer. JapanesePatent Application Laid-Open No. 55-146786 discloses that a coatinglayer formed of a water-soluble polymer is used.

In U.S. Pat. Nos. 4,879,166 and 5,104,730, and Japanese PatentApplication Laid-Open Nos. 2-276670, 4-37576 and 5-32037, there havebeen proposed recording sheets having a layer using an alumina hydrateof a pseudoboehmite structure.

As described in U.S. Pat. Nos. 4,374,804 and 5,104,730, and JapanesePatent Application Laid-Open Nos. 58-110287 and 4-37576, it has alsobeen conducted to form an ink-receiving layer of a multi-layer structureusing a silica or alumina material.

However, the conventional recording media have involved the followingproblems:

1) U.S. Pat. No. 5,104,730, and Japanese Patent Application Laid-OpenNos. 2-276670, 2-276671 and 3-275378 disclose recording media havingextremely narrow distribution of pore radius. As disclosed in JapanesePatent Application Laid-Open Nos. 4-267180 and 5-16517, however,individual dyes for inks (cyan, magenta, yellow and black) and solventsfor the inks are selectively adsorbed in pores of a specific size.Therefore, bleeding may occur on prints if the composition of ink ischanged.

The bleeding refers to a phenomenon that edges of boundaries ofmulti-color printed areas can not be resolved because of featheringcaused when ink is still fluid before it is fixed in the ink-receivinglayer.

2) U.S. Pat. No. 5,104,730, and Japanese Patent Application Laid-OpenNos. 2-276670, 2-276671 and 3-275378 disclose recording media havingpore radius distribution as narrow as 10 to 30 Å in average pore radius.In this pore radius distribution, dye adsorptiveness is good, while theabsorptiveness of solvent is insufficient, resulting in the occurrenceof beading.

The beading mentioned in the present invention refers to a phenomenon inwhich dots irregularly move in the plane direction of the surface of anink-receiving layer when ink is still fluid before it is fixed in theink-receiving layer, thus forming new aggregates together with adjacentdots to cause an unevenness in the density of recorded images.

3) In printing of color images, inks increase in quantity. The inksprinted cannot be completely absorbed in pores, but run out on thesurface of an ink-receiving layer, so that bleeding occurs, resulting indeterioration in print quality.

4) High-speed printing requires to have good drying ability. However,absorbing rate is insufficient, and the printed surface is hence not drywhen discharged out of a printing apparatus, so that output images maybe possibly impaired by contact.

5) There is a problem that the solids concentration of a dispersion of apigment or the like cannot be increased because the viscosity of thedispersion increases with time, resulting in a failure to apply it. As ameasure for the solution of the problem, Japanese Patent ApplicationLaid-Open No. 4-67986 discloses a process in which the polymerizationdegree of a polymer as a binder is lowered. However, this processinvolves problems of defective appearance such as cracking in anink-receiving layer, reduction in water fastness, and the like, andhence still requires a further improvement.

6) There is a problem that since the viscosity of the dispersion ishigh, its solids concentration cannot be increased. As a measure for thesolution of the problem, Japanese Patent Application Laid-Open No.4-67985 discloses a process in which an acid such as a monocarboxylicacid is added as a dispersant. However, this process is accompanied byproductive problems that offensive odor is given, and corrosion iscaused.

7) In order to improve ink absorptiveness and resolution of images, U.S.Pat. Nos. 4,780,356, 4,374,804 and 5,104,730, Japanese PatentPublication No. 3-72460, and Japanese Patent Application Laid-Open Nos.55-11829, 58-110287, 62-270378 and 4-37576 disclose a process in whichan ink-receiving layer of a two or more multi-layer structure is formed.However, the process involves a problem that coating and drying must beconducted at least twice for forming the ink-receiving layer, and so thenumber of processes increases. In addition, since the physical propertyvalues of the individual layers are different from each other, there arealso problems of changes with time, defective appearance such ascracking in the ink-receiving layer, and separation and peeling of thelayers from each other upon printing or the like.

8) Japanese Patent Application Laid-Open No. 3-281384 discloses analumina hydrate forming an aggregate like a needle, which is in the formof a column having an aspect ratio of not higher than 3 andunidirectionally oriented, and a process for forming an ink-receivinglayer using the alumina hydrate. However, since particles of the aluminahydrate are oriented and compacted, spaces among the alumina hydrateparticles in the ink-receiving layer tends to narrow. Therefore, thepore radius is partial to a narrow side, and distribution of pore radiushas a tendency to narrow. As a result, there is a problem that beadingoccurs as described above.

SUMMARY OF THE INVENTION

The present invention has thus been made with a view toward solving theabove problems and has as its object the provision of a recording mediumwhich can be suited to inks of various compositions, is excellent in inkabsorptiveness, can suppress feathering or bleeding of print andoccurrence of beading and can provide images high in optical density,and an ink-jet recording method using this recording medium.

Another object of the present invention is to provide a recording mediumwhich can effectively adsorb or absorb a dye and a solvent, which arecomponents for an ink, and hence permits good coloring and quick drying,and an ink-jet recording method using this recording medium.

A further object of the present invention is to provide a dispersion ofa pigment, which is suitable for use in production of the aboverecording media.

A still further object of the present invention is to provide arecording medium in which both dispersibility of a dispersion forcoating and dye-adsorbing ability are satisfied, an ink-jet recordingmethod using the recording medium, and a dispersion suitable for use inproduction of the recording medium.

The above objects can be achieved by the present invention describedbelow.

According to the present invention, there is thus provided a recordingmedium comprising an alumina hydrate having an average pore radius of 20to 200 Å and a half breadth of pore radius distribution of 20 to 150 Å.

According to the present invention, there is also provided a recordingmedium comprising a base material and an ink-receiving layer whichcomprises a pigment and a binder and is provided on the base material,wherein the pigment is an alumina hydrate and the ink-receiving layerhas an average pore radius of 20 to 200 Å and a half breadth of poreradius distribution of 20 to 150 Å.

According to the present invention, there is further provided arecording medium comprising principally pulp fibers and a filler,wherein the filler comprises an alumina hydrate having an average poreradius of 20 to 200 Å and a half breadth of pore radius distribution of20 to 150 Å.

According to the present invention, there is still further provided arecording medium comprising an alumina hydrate having at least two peaksin pore radius distribution.

According to the present invention, there is yet still further provideda recording medium comprising a base material and an ink-receiving layerwhich comprises a pigment and a binder and is provided on the basematerial, wherein the pigment comprises an alumina hydrate and theink-receiving layer has at least two peaks in pore radius distribution.

According to the present invention, there is still further provided arecording medium comprising principally pulp fibers and a filler,wherein the filler comprises an alumina hydrate having at least twopeaks in pore radius distribution.

According to the present invention, there is yet still further provideda recording medium comprising an alumina hydrate containing 0.01 to1.00% by weight of titanium dioxide.

According to the present invention, there is yet still further provideda recording medium comprising a base material and an ink-receiving layerwhich comprises an alumina hydrate containing 0.01 to 1.00% by weight oftitanium dioxide and is provided on the base material.

According to the present invention, there is still further provided arecording medium comprising principally pulp fibers and a filler,wherein the filler comprises an alumina hydrate containing 0.01 to 1.00%by weight of titanium dioxide.

According to the present invention, there is yet still further providedan ink-jet recording method comprising ejecting minute droplets of anink from an orifice to apply the droplets to a recording medium, therebyconducting printing, wherein one of the recording media described aboveis used as the recording medium.

According to the present invention, there is yet still further provideda dispersion of an alumina hydrate, which is obtained by dispersing analumina hydrate containing 0.1 to 1.0% by weight of a nitrate anion andhaving an average pore radius of 20 to 200 Å and a half breadth of poreradius distribution of 20 to 150 Å in deionized water, wherein thedispersion having a solids concentration of 15% by weight has aviscosity of not higher than 75 cP as measured at 20° C. and a shearrate of 7.9 sec⁻¹.

According to the present invention, there is yet still further provideda dispersion of an alumina hydrate, which is obtained by dispersing analumina hydrate containing 0.1 to 1.0% by weight of a nitrate anion andhaving at least two peaks in pore radius distribution in deionizedwater, wherein the dispersion having a solids concentration of 15% byweight has a viscosity of not higher than 75 cP as measured at 20° C.and a shear rate of 7.9 sec⁻¹.

According to the present invention, there is yet still further provideda dispersion of an alumina hydrate, which is obtained by dispersing atitanium dioxide-containing alumina hydrate containing 0.1 to 1.0% byweight of a nitrate anion in deionized water, wherein the dispersionhaving a solids concentration of 15% by weight has a viscosity of nothigher than 75 cP as measured at 20° C. and a shear rate of 7.9 sec⁻¹.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a recording medium according to thepresent invention.

FIG. 2 diagrammatically illustrates an X-ray diffraction pattern of analumina hydrate according to the present invention.

FIG. 3 is a photograph illustrating a crystal structure of the aluminahydrate according to the present invention.

FIG. 4 is a photograph illustrating the structure of particles of thealumina hydrate in an ink-receiving layer according to the presentinvention, viewed from the section of the ink-receiving layer.

FIG. 5 diagrammatically illustrates an isothermal adsorption curve of analumina hydrate used in the first aspect of the present invention.

FIG. 6 diagrammatically illustrates the pore radius distribution of thealumina hydrate used in the first aspect of the present invention.

FIG. 7 diagrammatically illustrates an isothermal adsorption curve of analumina hydrate used in the second aspect of the present invention.

FIG. 8 diagrammatically illustrates the pore radius distribution of thealumina hydrate used in the second aspect of the present invention.

FIGS. 9A and 9B are cross-sectional views illustrating a contained typeand a mixed type, respectively, of pore portions in recording media inthe third aspect of the present invention.

FIG. 10 diagrammatically illustrates an isothermal adsorption curve of atitanium dioxide-containing alumina hydrate used in the third aspect ofthe present invention.

FIG. 11 diagrammatically illustrates the pore radius distribution of thetitanium dioxide-containing alumina hydrate used in the third aspect ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a recording medium (first aspect)comprising, as an essential component, at least an alumina hydratehaving the average pore radius and half breadth of pore radiusdistribution within the specific ranges described above, a recordingmedium (second aspect) comprising, as an essential component, at leastan alumina hydrate having the above-described feature in pore radiusdistribution, and a recording medium (third aspect) comprising, as anessential component, at least an alumina hydrate containing titaniumdioxide in the specific amount described above. Each of these recordingmedia is constituted by, for example, internally containing itscorresponding alumina hydrate in a sheet such as paper at a stage inwhich the sheet is formed from a raw material, or forming anink-receiving layer composed principally of the alumina hydrate and abinder on a base material as illustrated in FIG. 1. The alumina hydratesare most preferable, in particular, as a material used in theink-receiving layer because it has a positive charge, so that a dye inan ink is well fixed and an image good in coloring is hence provided,and moreover there are no problems of bronzing and light fastness, whichhave heretofore been caused by the use of silica compounds. A phenomenoncalled "bronzing" in which the hue of a black recorded area looksbrownish has presented itself, and a new problem has hence been offered.

The alumina hydrates used in the recording media according to thepresent invention may preferably be non-crystalline as analyzed by theX-ray diffraction method.

The alumina hydrate is defined by the following general formula:

    Al.sub.2 O.sub.3-n (OH).sub.2n.mH.sub.2 O

wherein n is an integer of 0, 1, 2 or 3, m is a number of 0 to 10,preferably 0 to 5. In many cases, mH₂ O represents an aqueous phasewhich does not participate in the formation of a crystal lattice, but isable to eliminate. Therefore, m may take a value other than an integer.Besides, m may take a value of 0 when a material of this kind iscalcinated.

The alumina hydrate can be produced by any conventional method such asthe hydrolysis of aluminum alkoxide or sodium aluminate. Rocek, et al.Collect Czech. Chem. Commun., Vol. 56, 1253-1262 (1991)! have reportedthat the pore structure of aluminum hydroxide is affected by depositiontemperature, pH of the solution, aging time and a kind of surfactantsused.

For example, KODANSHA LTD PUBLISHERS, "Shokubai Koza (The CatalystCourse)", Vol. 5, Chapter on Engineering, Design of Catalysts, 123(1985) describes an alumina hydrate as generally having one peak in poreradius distribution. Further, Kobayashi "Surface", Vol. 15, 282 (1977)!has also reported that an alumina hydrate has one peak in pore radiusdistribution. Rocek, et al. Collect Czech. Chem. Commun., 56(6),1263-1269 (1991)! have reported that aluminum hydroxide deposited at arelatively low temperature of 30 to 50° C. and pH 7 to 8 shows atwo-peak porous structure having peaks in a large pore region and amedium pore region.

The shape of the alumina hydrate used in the present invention ispreferably in the form of a flat plate and has an average aspect ratioof 3 to 10 and a slenderness ratio of a flat plate surface of 0.6 to1.0. The definition of the aspect ratio can be given by the methoddescribed in Japanese Patent Publication No. 5-16015. The aspect ratiois expressed by a ratio of "diameter" to "thickness" of a particle. Theterm "diameter" as used herein means a diameter of a circle having anarea equal to a projected area of the particle, which has been obtainedby observing the alumina hydrate through a microscope or a TEM. Theslenderness ratio means a ratio of a minimum diameter to a maximumdiameter of the flat plate surface when observed in the same manner asin the aspect ratio. If the average aspect ratio is lower than the lowerlimit of the above range, the range of the pore radius distribution ofthe ink-receiving layer narrows. On the other hand, average aspectratios higher than the upper limit of the above range makes it difficultto produce the alumina hydrate with its particle size even. If theaverage slenderness ratio is lower than the lower limit of the aboverange, the range of the pore radius distribution similarly narrows. Asdescribed in the literature Rocek J., et al., Applied Catalysis, Vol.74, 29-36 (1991)!, it is generally known that pseudoboehmite amongalumina hydrates has both needle form and another form.

According to a finding of the present inventor, the alumina hydrate in aflat plate form is more preferred because it has better dispersibilitythan that of a needle form (the ciliary form), and the orientation ofparticles of the alumina hydrate becomes random as illustrated in thephotograph in FIG. 4 when forming an ink-receiving layer, so that therange of the pore radius distribution widens.

In Handbook of Paper Processing, p. 402, there is described particles ofaluminum hydroxide as being in the form of a hexagonal flat plate.Besides this, alumina hydroxides such as HIGILITE (trade name, productof Showa Denko K.K.) and HYDRAL (trade name, product of ALCOA) areknown. Further, Japanese Patent Application Laid-Open No. 2-276670discloses an alumina sol in the form of a needle having an aspect ratioof 2 to 10, while Japanese Patent Application Laid-Open No. 3-285814discloses a boehmite sol in the form of a plate having an aspect ratioof 2 to 10. However, none of these documents disclose a relationshipbetween the shape of the alumina hydrate and the pore structure ordispersibility of particles thereof as described below.

The BET surface area of each of the alumina hydrates, the pore radiusdistributions of the alumina hydrate and the ink-receiving layercontaining the alumina hydrate, and pore volumes and isothermaladsorption and desorption curves as described below can be obtained atthe same time by the nitrogen adsorption and desorption method. The BETspecific surface areas of the alumina hydrates used in the presentinvention may preferably be within a range of from 70 to 300 m² /g. Ifthe BET specific surface area is smaller than the lower limit of theabove range, the pore radius distribution is partial to a large side. Asa result, a dye in an ink cannot be fully adsorbed and fixed. On theother hand, surface areas greater than the upper limit of the aboverange result in failures to apply the pigment with good dispersibilityand hence to control the pore radius distribution.

No particular limitation is imposed on the production process of thealumina hydrates used in the present invention. However, it ispreferable to use a process capable of producing a non-crystal aluminahydrate. For example, either of the Bayer's process or the alumpyrolysis process may be used.

As a process for the production of the non-crystal alumina hydrate,which can be particularly preferably used in the present invention, maybe mentioned a process in which an acid is added to an aluminumlong-chain alkoxide to hydrolyze the alkoxide, thereby obtaining analumina hydroxide. The term "aluminum long-chain alkoxide" as usedherein means an alkoxide having, for example, 5 or, more carbon atoms.Further, the use of an alkoxide having 12 to 22 carbon atoms ispreferred because the removal of alcohol formed and the shape control ofthe alumina hydrate can be conducted with ease. The process has anadvantage that impurities such as various ions are hard to get mixedcompared with the process for producing alumina hydrogel or cationicalumina. The aluminum long-chain alkoxide also has an advantage thatsince the alcohol formed is easy to remove after the hydrolysis, theremoval of the alcohol from the alumina hydrate can be completelyconducted compared with the case where a short-chain alkoxide such asaluminum isopropoxide is used. Further, in the process making use of thealuminum long-chain alkoxide, particles of the alumina hydrate obtainedby the hydrolysis tend to be in the form of a flat plate, and so theshape of the particles is easy to control. In this process, it ispreferable from a viewpoint of obtaining the non-crystal alumina hydrateto preset the pH of a solution to 6 or lower upon the initiation of thehydrolysis. If the pH is more than 8, the alumina hydrate to be finallyobtained will become crystalline.

The alumina hydrate used in the first aspect of the present inventionobtained by the above process is subjected to a hydrothermal synthesisto grow its particles (aging process). The conditions of the agingprocess can be suitably adjusted to control the pore form of the aluminahydrate particles within a specific range. If the time of the aging istoo short, primary particles of the alumina hydrate, which arerelatively uneven in particle size, grow, and so the sizes of spacesamong the primary particles, which the spaces define pores, becomeuneven. As a result, it is considered that the range of pore radiusdistribution widens. The correlation between the degree of unevenness ofthe primary particles and the range of the pore radius distribution isunclear. The sol obtained may be used as a dispersion as it is asdisclosed in Japanese Patent Application Laid-Open No. 2-276670. In thepresent invention, it is however preferable to dry the sol once intopowder by a method such as spray drying and then prepare a dispersion.In this case, the dispersibility of the alumina hydrate in water is moreenhanced.

The best feature of the alumina hydrate used in the third aspect of thepresent invention is to contain titanium dioxide in a specificproportion. The content thereof is preferably within a range of from0.01 to 1.00% by weight, more preferably from 0.13 to 1.00% by weight.Further, the valence of titanium in the titanium dioxide is preferably+4.

According to another finding of the present inventor, the titaniumdioxide contained exists on the surface of the alumina hydrate in theform of such ultrafine particles that they cannot be observed through anelectron microscope of 500,000 magnifications, and serves as anadsorption site upon the adsorption of the dye in the ink. The reason ofthat is not clearly understood. As reported by Yang, et al. React.Kinet. Catal. Lett., 46(1), 179-186 (1992)!, it is however inferred thattwisted sites containing strongly electron-acceptable Al³⁺ are formed bythe addition of titanium dioxide, and the dye-adsorbing ability is henceimproved, or the titanium ion of titanium dioxide forms a coordinatebond with the dye.

According to a further finding of the present inventor, the valence ofthe titanium is +4 judged from the value of bound energy by theobservation of ESCA. Since no splitting occurs on 3p peak for titaniumand 2p peak for aluminum, there is no interaction between titanium andaluminum. Namely, titanium dioxide solely exists without interactingbetween titanium and aluminum. When the surface of the titaniumdioxide-containing alumina hydrate is etched with argon, the amount oftitanium is decreased to half in the etching time of about 100 seconds.No titanium is detected in the etching time of about 500 seconds.Therefore, the titanium dioxide exists only in the vicinity of thesurfaces of the alumina hydrate particles without affecting the surfacecharge of the alumina hydrate under the conditions of the particle size,valence and splitting of peaks, so that the dispersibility of thealumina hydrate is not impaired.

If the valence of titanium in the titanium dioxide becomes lower than+4, the titanium dioxide comes to serve as a catalyst by lightirradiation and the binder is hence deteriorated, so that cracking anddusting tends to occur. The alumina hydrate used in the third aspect ofthe present invention may contain the titanium dioxide either only inthe vicinity of the surfaces of the alumina hydrate particles or up tothe interiors thereof. Its content may be changed from the surface tothe interior. As demonstrated in Examples of the present invention,which will be described subsequently, the titanium dioxide maypreferably be contained only in the close vicinity of the surfaces ofthe particles because the bulk properties of the interior of the aluminahydrate are easy to be kept in the vicinity of the surface, therebyundergoing no change in dispersibility.

Although oxides of magnesium, calcium, strontium, barium, zinc, boron,silicon, germanium, tin, lead, zirconium, indium, phosphorus, vanadium,niobium, tantalum, chromium, molybdenum, tungsten, manganese, iron,cobalt, nickel, ruthenium and the like may be used instead of thetitanium dioxide. However, the titanium dioxide is most preferred fromthe viewpoint of the adsorptiveness of a dye in an ink anddispersibility. Most of the oxides of the above-mentioned metals arecolored, while the titanium dioxide is colorless. From this point, thetitanium dioxide is also preferred.

The titanium dioxide-containing alumina hydrate used in the third aspectof the present invention may preferably be of a non-crystallinestructure as analyzed by the X-ray diffraction method.

As a process for producing the titanium dioxide-containing aluminahydrate, a process in which a liquid mixture of an aluminum alkoxide anda titanium alkoxide is hydrolyzed is most preferred because the particlesize of titanium dioxide can be made small and is easy to control. Theparticle size and shape in this process are discussed in the form of anNi/Al₂ O₃ catalyst by an alkoxide process in, for example, GakkaiShuppan Center, "Science of Surfaces", edited by Kenji Tamaru, 327(1985). As another process, its production may also be conducted byadding an alumina hydrate as a nucleus for crystal growth upon thehydrolysis of the mixture of the aluminum alkoxide and the titaniumalkoxide. In this process, the titanium dioxide exists only in thevicinity of the surface of the alumina hydrate.

Materials with a variety of materials supported on surfaces of particlessuch as alumina are widely known in the field of catalysts. Titaniumdioxide is poor in solubility in solvents such as water, and henceextremely hard to be supported on alumina or the like. It is known tosupport titanium as a soluble salt on the surfaces of alumina hydrateparticles. It is however difficult to convert the titanium compoundsupported on the surfaces of the hydrate particles to titanium dioxideand also to remove the counter ion component by which the titanium salthas been formed. In general, the valence of the titanium compoundsupported is smaller than +4. Therefore, the valence of titanium asdetermined by ESCA is not +4 like the titanium dioxide-containingalumina hydrate according to the third aspect of the present invention.

Dispersions of the above-described alumina hydrates used in the first tothird aspects of the present invention may be used either as an additive(for example, added to a pulp slurry upon the preparation of a rawmaterial for paper making) upon the production of the respectiverecording media, more specifically, upon the production of paper, or asa coating dispersion for forming an ink-receiving layer on a basematerial.

In the recording medium used in the first to third aspects of thepresent invention according to an embodiment of the present invention, acoating dispersion (a dispersion of the alumina hydrate) containing thealumina hydrate as a pigment and a binder is applied to a base materialto form an ink-receiving layer. The values of physical properties of theink-receiving layer are not determined only by the alumina hydrate, butchanged by various production conditions such as the kind and mixingamount of the binder, the concentration, viscosity and dispersion stateof the coating dispersion, coating equipment, coating head, coatingweight, and the flow rate, temperature and blowing direction of dryingair. it is therefore necessary to control the production conditionswithin the optimum limits for achieving the properties of theink-receiving layer according to the present invention.

The alumina hydrate used in the first aspect of the present invention iswide in the half breadth of pore radius distribution, which will bedescribed subsequently, and is dispersed up to a level of primaryparticles in a dispersion for coating. Such wide pore radiusdistribution is substantially kept even after the formation of theink-receiving layer through steps of dispersion of the alumina hydrate,coating on the base material and drying. The reason of this is notclearly understood. The present inventor however dares to explain forfacilitating the understanding of the present invention, and infers thata pore structure is defined principally by spaces among the primaryparticles of the alumina hydrate, and the alumina hydrate particles inthe form of a flat plate are oriented at random in the ink-receivinglayer, or that the wide pore radius distribution attributable to theunevenness of the particle size of the alumina hydrate is kept even inthe ink-receiving layer.

The average pore radius of the ink-receiving layer is preferably withina range of from 20 to 200 Å, while its half breadth of pore radiusdistribution is preferably within a range of from 20 to 150 Å, morepreferably from 80 to 150 Å. The term "half breadth of pore radiusdistribution" as used herein means a breadth of pore radius which is amagnitude half of the magnitude of the average pore radius. If theaverage pore radius is larger than the upper limit of the above range,the resulting recording medium is deteriorated in the adsorption andfixing of a dye in an ink, and so bleeding tends to occur on images. Ifthe average pore radius is smaller than the lower limit of the aboverange, the resulting recording medium is deteriorated in inkabsorptiveness, and so beading tends to occur. On the other hand, if thehalf breadth is outside of this range, the resulting recording medium isdeteriorated in the adsorption of a dye or a solvent in an ink.

As with the ink-receiving layer, the pore radius distribution of thealumina hydrate making up the ink-receiving layer preferably has anaverage pore radius of 20 to 200 Å and a half breadth of pore radiusdistribution of 20 to 150 Å. The pore radius distribution of theink-receiving layer depends upon the pore radius distribution of thealumina hydrate. Therefore, if the pore radius distribution of thealumina hydrate is outside the above range, the pore radius distributionof the ink-receiving layer cannot be controlled within the above range.

In the first aspect, the pore volume of the ink-receiving layer ispreferably within a range of from 0.4 to 0.6 cc/g. If the pore volume ofthe ink-receiving layer is greater than the upper limit of the aboverange, cracking and dusting occur on the ink-receiving layer. If thepore volume is smaller than the lower limit of the above range, theresulting recording medium is deteriorated in ink absorption. The totalpore volume of the ink-receiving layer is more preferably at least 8cc/m². If the total pore volume is smaller than this limit, inks tend torun out of the ink-receiving layer when multi-color printing isconducted, and so bleeding occurs on images. As with the ink-receivinglayer, the pore volume of the alumina hydrate making up theink-receiving layer is preferably within a range of from 0.4 to 0.6cc/g. If the pore volume of the alumina hydrate is outside the aboverange, the pore volume of the ink-receiving layer cannot be controlledwithin the above range.

The alumina hydrate obtained by the above process is subjected to ahydrothermal synthesis, thereby its particles grow (an aging step). Bycontrolling the conditions of this step, the pore form of the aluminahydrate particles can be controlled within a specified range. Uponsetting an aging time suitable, primary particles of the alumina hydratehaving relatively even particle size grow, so that the sizes of spacesamong the primary particles, which define pores, become even and therange of pore radius distribution becomes narrow. If the aging time ismade longer than that conditions, the alumina hydrate having two tops inthe pore radius distribution can be obtained. As a result, a recordingmedium, in which two tops are made in the pore radius distribution ofalumina hydrate, can be obtained. The sol obtained may be used as adispersion as it is as disclosed in Japanese Patent ApplicationLaid-Open No. 2-276670. In the present invention, it is howeverpreferable to dry the sol once into powder by a method such as spraydrying and then prepare a dispersion. In this case, the dispersibilityof the alumina hydrate in water is more enhanced.

The alumina hydrate obtained by the process has two or more peaks in apore radius distribution. A pore structure is mainly formed by spacesamong the primary structure is mainly formed by spaces among the primaryparticles of the alumina hydrate. The reason why the pore radiusdistribution has at least two peaks is considered to be as follows.Since the alumina hydrate particles are in the form of a flat plate andthe primary particles are oriented at random in the dried powder, thereare defined spaces of portions in which primary particles overlap witheach other in a direction of the principal plain of the flat plate andspaces of another portions in which an end face and the principal planeor another end face overlap with each other. Thus, two or more peaks inthe pore radius distribution are all caused by the spaces among theprimary particles, and at least one of the pore radii at one peakbecomes smaller than the minor axis or major axis radius of the flatplate surface of the primary particles, while at least one of the poreradii at another peaks becomes about several times the minor axis ormajor axis radius of the flat plate surface.

The alumina hydrate of the present invention is, as described above, hasat least two peaks in the pore radius distribution. Although such thealumina hydrate is dispersed up to a level of primary particles in adispersion for coating, the radius distribution having at least onepeaks is kept substantially even when the ink-receiving layer is formedthrough the steps of dispersing of the alumina hydrate, coating onto asubstrate and drying. The reason is considered as follows: Even in anink-receiving layer, the primary particles of the alumina hydrate areoriented in random direction, as shown by the photograph in FIG. 3, andtherefore, as same as in a case of titanium dioxide-containing aluminahydrate, there are generated spaces of portions in which primaryparticles overlap with each other in a direction of the principal plainof the flat plate through a binder and spaces of another portions inwhich an end face and the principal plane or another end fade overlapwith each other through a binder, by which the pore radius distributionhaving two or more peaks is kept even when the ink-receiving layer isformed therefrom.

Japanese Patent Application Laid-Open No. 58-110287 discloses arecording sheet having peaks of pore radius at 0.05 μm or smaller and arange of from 0.2 to 10 μm. However, the former peak is caused by thespaces among primary particles, while the latter peak is defined by thespaces among secondary, tertiary or higher-order particles aggregated bythe primary particles. Therefore, this sheet is different from therecording medium according to the second aspect of the presentinvention, in which said at least two peaks are caused by the spacesamong primary particles. Accordingly, the positions of the peaks of thepore radii are quite different from those of the second aspect of thepresent invention.

In the recording medium according to the second aspect of the presentinvention, the ink-receiving layer also has at least two peaks in thepore radius distribution. The solvent component in an ink is absorbed byrelatively large pores, while the dye in the ink is adsorbed byrelatively small pores. The pore radius corresponding to one of thepeaks is preferably smaller than 100 Å, more preferably 10 to 60 Å. Thepore radius corresponding to another peak is preferably within a rangeof from 100 to 200 Å. If the pore radius corresponding to the formerpeak is larger than the above limit, the resulting recording medium isdeteriorated in the adsorption and fixing of the dye in the ink, and sobleeding and beading occur on images. If the pore radius correspondingto the latter peak is smaller than the lower limit of the above range,the resulting recording medium is deteriorated in the absorption of thesolvent component in the ink, so that the ink is not well dried, and thesurface of the ink-receiving layer remains wet even when the medium isdischarged out of a printer after printing. If the pore radiuscorresponding to the latter peak is greater than the upper limit of theabove range, the resulting ink-receiving layer tends to crack.

In the second aspect of the present invention, the alumina hydrate alsohas at least two peaks in the pore radius distribution. As with theink-receiving layer, in the pore radius distribution, the pore radiuscorresponding to one of relatively small peaks is preferably smallerthan 100 Å, more preferably 10 to 60 Å. The pore radius corresponding toa relatively large peak is preferably within a range of from 100 to 200Å. As described above, the pore structure is defined by the primaryparticles of the alumina hydrate. The nature of this pore structure isalready created by the alumina hydrate. Therefore, if the pore radiicorresponding to the peaks of the pore radius distribution of thealumina hydrate are outside the above ranges, the pore radiicorresponding to the peaks of the pore radius distribution of theink-receiving layer cannot be controlled within the above range.

In the second aspect, the pore volume of the ink-receiving layer ispreferably within a range of from 0.1 to 1.0 cc/g, more preferably from0.4 to 0.6 cc/g. If the pore volume of the ink-receiving layer isgreater than the upper limit of the above range, cracking and dustingoccur on the ink-receiving layer. If the pore volume is smaller than thelower limit of the above range, the resulting recording medium isdeteriorated in ink absorption. The total pore volume of theink-receiving layer is more preferably at least 8 cc/m². If the totalpore volume is smaller than this limit, inks tend to run out of theink-receiving layer when multi-color printing is conducted, and sobleeding occurs on images. The pore volume of pores having a peak at apore radius of smaller than 100 Å is preferably within a range of from0.1 to 10% by volume, more preferably from 1 to 5% by volume based onthe total pore volume.

The pore volume of the pores having the peak at a pore radius of smallerthan 100 Å means a pore volume within a range showing a breadth of poreradii having a magnitude half of the greatest-magnitude pore radius ofthe pores having a peak at smaller than 100 Å in the pore radiusdistribution. If the pore volume of the pores having a peak at a poreradius of smaller than 100 Å in the ink-receiving layer is smaller thanthe lower limit of the above range, the resulting recording medium isdeteriorated in adsorption of a dye in an ink. If the pore volumeexceeds the upper limit of the above range, the resulting recordingmedium is deteriorated in the absorption of the solvent component in theink. The pore volume of the alumina hydrate is also preferably within arange of from 0.1 to 1.0 cc/g, more preferably from 0.4 to 0.6 cc/g. Thepore volume of pores having a peak at a pore radius of smaller than 100Å is preferably within a range of from 0.1 to 10% by volume, morepreferably from 1 to 5% by volume based on the total pore volume. Thepore volume of the ink-receiving layer depends upon the pore volume ofthe alumina hydrate. Therefore, if the pore volume of the aluminahydrate is outside the above range, the pore volume of the ink-receivinglayer cannot be controlled within the above range.

In the third aspect of the present invention, the titaniumdioxide-containing alumina hydrate is wide in the half breadth of poreradius distribution as described below. Such an alumina hydrate isdispersed up to a level of primary particles in a dispersion forcoating. Such wide pore radius distribution is substantially kept evenafter the formation of the ink-receiving layer through steps ofdispersion of the alumina hydrate, coating on the base material anddrying. The reason of this is not clearly understood, but is consideredto be as described above.

The average pore radius of the ink-receiving layer is preferably withina range of from 20 to 200 Å, while its half breadth of pore radiusdistribution is preferably within a range of from 20 to 150 Å, morepreferably from 80 to 150 Å.

If the average pore radius is larger than the upper limit of the aboverange, the resulting recording medium is deteriorated in the adsorptionand fixing of a dye in an ink, and so bleeding tends to occur on images.If the average pore radius is smaller than the lower limit of the aboverange, the resulting recording medium is deteriorated in inkabsorptiveness, and so beading tends to occur. On the other hand, if thehalf breadth is outside of this range, the resulting medium isdeteriorated in the adsorption of a dye or a solvent system. As with theink-receiving layer, the pore radius distribution of the alumina hydratepreferably has an average pore radius of 20 to 200 Å and a half breadthof pore radius distribution of 20 to 150 Å. The pore radius distributionof the ink-receiving layer depends upon the pore radius distribution ofthe alumina hydrate. Therefore, if the pore radius distribution of thealumina hydrate is outside the above range, the pore radius distributionof the ink-receiving layer cannot be controlled within the above range.

The pore volume of the ink-receiving layer is preferably within a rangeof from 0.4 to 0.6 cc/g. If the pore volume of the ink-receiving layeris greater than the upper limit of the above range, cracking and dustingoccur on the ink-receiving layer. If the pore volume is smaller than thelower limit of the above range, the resulting recording medium isdeteriorated in ink absorption. The total pore volume of theink-receiving layer is more preferably at least 8 cc/m². If the totalpore volume is smaller than this limit, inks tend to run out of theink-receiving layer when multi-color printing is conducted, and sobleeding occurs on images. As with the ink-receiving layer, the porevolume of the alumina hydrate is preferably within a range of from 0.4to 0.6 cc/g. If the pore volume of the alumina hydrate is outside theabove range, the pore volume of the ink-receiving layer cannot becontrolled within the above range.

In the preferred embodiment, the titanium dioxide-containing aluminahydrate has at least two peaks in the pore radius distribution. Thealumina hydrate is dispersed up to a level of primary particles in adispersion for coating. The pore radius distribution having at least twopeaks is not lost at all even when the ink-receiving layer is formedtherefrom. Such pore structure as described above is defined principallyby spaces among the primary particles of the alumina hydrate. The reasonwhy the pore radius distribution has at least two peaks is considered tobe as described above. As described above, pores corresponding to saidat least two peaks in the pore radius distribution are all caused by thespaces among the primary particles. At least one of the pore radii atone peak becomes smaller than the minor axis or major axis radius of theflat plate surface of the primary particles, while at least one of thepore radii at another peak becomes about several times the minor axis ormajor axis radius of the flat plate surface.

In the third aspect of the present invention, the ink-receiving layeralso has at least two peaks in the pore radius distribution. The solventcomponent in an ink is absorbed by relatively large pores, while the dyein the ink is adsorbed by relatively small pores. The pore radiuscorresponding to one of relatively small peaks is preferably smallerthan 100 Å, with 10 to 60 Å being more preferred because thedye-adsorbing ability is markedly improved. The-pore radiuscorresponding to a relatively large peak is preferably within a range offrom 100 to 200 Å because the rate of absorption of the solvent becomesfast. If the pore radius corresponding to the relatively small peak islarger than the above limit, the resulting recording medium isdeteriorated in the adsorption and fixing of the dye in the ink, and sobleeding and beading occur on images. If the pore radius correspondingto the relatively large peak is smaller than the lower limit of theabove range, the resulting recording medium is deteriorated in theabsorption of the solvent component in the ink, so that the ink is notwell dried, and the surface of the ink-receiving layer remains wet evenwhen the medium is discharged out of a printer after printing. If thepore radius corresponding to the latter peak is greater than the upperlimit of the above range, the resulting ink-receiving layer tends tocrack.

In the third aspect of the present invention, the alumina hydrate alsohas at least two peaks in the pore radius distribution. As with theink-receiving layer, in the pore radius distribution, the pore radiuscorresponding to one of relatively small peaks is preferably smallerthan 100 Å, more preferably 10 to 60 Å. The pore radius corresponding toa relatively large peak is preferably within a range of from 100 to 200Å. As described above, the pore structure is defined by the primaryparticles of the alumina hydrate. The nature of this pore structure isalready created by the alumina hydrate. Therefore, if the pore radiicorresponding to the peaks of the pore radius distribution of thealumina hydrate are outside the above ranges, the pore radiicorresponding to the peaks of the pore radius distribution of theink-receiving layer cannot be controlled within the above range.

In the third aspect, the pore volume of the ink-receiving layer ispreferably within a range of from 0.1 to 1.0 cc/g, more preferably from0.4 to 0.6 cc/g. If the pore volume of the ink-receiving layer isgreater than the upper limit of the above range, cracking and dustingoccur on the ink-receiving layer. If the pore volume is smaller than thelower limit of the above range, the resulting recording medium isdeteriorated in ink absorption. The total pore volume of theink-receiving layer is more preferably at least 8 cc/m². If the totalpore volume is smaller than this limit, inks tend to run out of theink-receiving layer when multi-color printing is conducted, and sobleeding occurs on images. The pore volume of pores having a peak at apore radius of smaller than 100 Å is preferably within a range of from0.1 to 10% by volume, more preferably from 1 to 5% by volume based onthe total pore volume.

As with the ink-receiving layer, the pore volume of the alumina hydrateis also preferably within a range of from 0.1 to 1.0 cc/g, morepreferably from 0.4 to 0.6 cc/g. Further, the pore volume of poreshaving a peak at a pore radius of smaller than 100 Å is preferablywithin a range of from 0.1 to 10% by volume, more preferably from 1 to5% by volume based on the total pore volume. The pore volume of theink-receiving layer depends upon the pore volume of the alumina hydrate.Therefore, if the pore volume of the alumina hydrate is outside theabove range, the pore volume of the ink-receiving layer cannot becontrolled within the above range.

In the recording media according to the first to third aspect of thepresent invention, which each have an ink-receiving layer on a basematerial, a relative pressure difference (ΔP) between adsorption anddesorption at 90 percent of the maximum amount of adsorbed gas as foundfrom an isothermal nitrogen adsorption and desorption curve for theink-receiving layer, which is 10 derived from the nitrogen adsorptionand desorption method, is preferably not larger than 0.2, morepreferably not larger than 0.15, most preferably not larger than 0.10.As described in McBain J. Am. Chem. Soc., Vol. 57, 699 (1935)!, therelative pressure difference (ΔP) can be used as an index whether a porein the form of an inkpot may exist. The pore is closer to a straighttube as the relative pressure difference (ΔP) is smaller. On the otherhand, the pore is closer to an inkpot as the difference is greater.Differences exceeding the above limit result in a recording medium poorin dryness of an ink after printing. Japanese Patent ApplicationLaid-Open No. 60-245588 describes the fact that with respect to theshape of pores in an alumina xerogel used in an ink-receiving layer,those low in degree of labyrinth, even and linear are preferred, whilean inkpot form narrow in inlet, a gourd form constricted in the middleand a winding form are not preferred from the viewpoint of rate ofabsorption. However, this publication does not disclose anything aboutspecific methods for measuring actual physical properties and the like.

With respect to the above-described alumina hydrates in the recordingmedia according to the first to third aspect of the present invention, arelative pressure difference (ΔP) between adsorption and desorption at90 percent of the maximum amount of adsorbed gas as found from anisothermal nitrogen adsorption and desorption curve for each of thealumina hydrates, which is derived from the nitrogen adsorption anddesorption method, is preferably not larger than 0.2, more preferablynot larger than 0.15, most preferably not larger than 0.10. If thedifference is outside this limit, the relative pressure difference (ΔP)of the ink-receiving layer as found from the isothermal nitrogenadsorption and desorption curve cannot be controlled within the abovelimit.

In the recording media according to the first to third aspect of thepresent invention, the number of hydroxyl groups on the surface of eachof the alumina hydrates is preferably at least 10²⁰ groups/g. If thenumber is fewer than this value, the solids concentration of adispersion in which the alumina hydrate is dispersed in water cannot beincreased. Such number of hydroxyl groups on the surface of the aluminahydrate can be determined by the titration with a triethylaluminumsolution.

The surface potential of each of the alumina hydrates used in thepresent invention can be determined by a zeta potential analyzer.Japanese Patent Application Laid-Open No. 60-232990 discloses thatalumina compounds have a positive charge, and in its Examples, thevalues of zeta-potentials. However, specific measuring method andconditions are not described therein. The value of a zeta-potentialvaries depending upon the cell and electrode structure in a measuringapparatus, applied voltage, the solids concentration and pH of adispersion, and dispersants and additives used. Therefore, absolutevalues cannot be directly compared unless the measuring conditions,apparatus and the like are standardized to conduct the measurement.

With respect to the alumina hydrates used in the present invention, thezeta-potential is preferably at least 15 mV as measured at pH 6 in theform of a 0.1% by weight aqueous dispersion free from any dispersant andadditive. If the zeta-potential is above this limit, the alumina hydratecan be easily dispersed up to a level of primary particles in adispersion. If the zeta-potential is lower than 15 mV, aggregate anddeposit occur as the solids concentration increases, or particles partlyaggregate to form great lumps when a binder dispersion is mixed with thealumina hydrate. For this reason, in particular, in the recording mediahaving an ink-receiving layer, pore radius of the ink-receiving layerbecomes markedly large, and so the strength of the ink-receiving layeris lowered, resulting in a potential problem that dusting may occur, ordye-fixing ability upon printing may be deteriorated. In general,alumina hydrate is stable in a low pH region. It is therefore known toadd an acid to low the pH of the dispersion. However, the addition ofthe acid is not preferred from the viewpoint of the occurrence ofoffensive odor and corrosion and of the limitation of the kind of binderused. Further, a known process in which a dispersant is added is notpreferred because repellent or the like occurs upon the coating of thedispersion.

On the other hand, if the pH region becomes higher, primary particlesaggregate according to the kind of the alumina hydrate to enlarge theparticle size, so that the alumina hydrate may apparently have a highzeta-potential in some cases. The zeta-potential recited in the presentinvention should be measured in a condition that such aggregation ofparticles does not occur. In order to determine whether such aggregationof particles occurs or not, it is effective to measure the particle sizeof dispersed particles. Any known method may be used as a measuringmethod of the particle size. It is necessary to confirm that theparticle size of particles in a dispersion kept at pH 6, which issubjected to the measurement of zeta-potential, has substantially thesame value as the particle size of particles in a dispersion kept at pH4 in which the particles are said to be stably dispersed.

In the present invention, a dispersion obtained by dispersing an aluminahydrate containing 0.1 to 1.0% by weight of a nitrate anion, saidalumina hydrate being such a specific alumina hydrate as describedabove, in deionized water to give a solids concentration of 15% byweight preferably has a viscosity of not higher than 75 cP, mostpreferably not higher than 30 cP as measured at 20° C. and a shear rateof 7.9 sec⁻¹. Further, a dispersion obtained by dispersing the samealumina hydrate containing 0.1 to 1.0% by weight of a nitrate anion asdescribed above in deionized water to give a solids concentration of 20%by weight preferably has a viscosity of not higher than 100 cP, mostpreferably not higher than 80 cP as measured at 20° C. and a shear rateof 10.2 sec⁻¹. Furthermore, a dispersion obtained by dispersing the samealumina hydrate containing 0.1 to 1.0% by weight of a nitrate anion asdescribed above in deionized water to give a solids concentration of 25%by weight preferably has a viscosity of not higher than 500 cP, mostpreferably not higher than 460 cP as measured at 20° C. and a shear rateof 10.2 sec⁻¹. In each of the above cases, if the viscosity exceeds theupper limit, the dispersion is required to low its solids concentration.It is not hence preferable from the viewpoint of mass productivity toincrease the viscosity beyond the above limit.

The viscosities of the alumina hydrate dispersions according to thepresent invention can be measured by means of a rotational viscometer,for example, a Brookfield type viscometer.

The prior art making use of the pseudoboehmite cited above and thepresent invention have been investigated in comparison with each other.As a result, differences therebetween are as follows:

1) With respect to the pore radius distribution in the prior art, thebreadth of the pore radius distribution is disclosed only in a narrowrange as demonstrated by the fact that the pore volume of pores within arange of the average pore radius ±10 Å amounts to 45 to 55% of the totalpore volume. On the contrary, the present inventor has found that whenthe breadth of the pore radius distribution is widened as describedherein, print quality remains unchanged even if the proportion of a dyeto a solvent in an ink and the composition of materials are hanged.

It has also been found that when one gets the pore radius distributionto have at least two peaks to divide the function of the pores, thesolvent component in an ink is absorbed in pores having a relativelylarge radius, while the dye component in the ink is adsorbed on poreshaving a relatively small radius, whereby a recording medium, by whichinks are quickly dried and good coloring is achieved even when amulti-color printing is conducted at high speed, is provided.

2) With respect to the pore radius and pore volume, the prior artdescribes the total pore volumes as being 0.2 to 1.0 cc/g for poreshaving a pore radius of 10 to 40Å, 0.1 to 0.4 cc/g for pores having apore radius of 40 to 100 Å, and 0.1 cc/g for pores having a pore radiusof 100 to 1000 Å. On the contrary, the present inventor has found thatwhen the relationship between the pore volume per unit area of theink-receiving layer and the isothermal nitrogen adsorption anddesorption curve thereof is adjusted within the range described herein,the adsorption and drying of the ink after printing are markedlyimproved.

3) The prior art describes a pseudoboehmite sol in the form of a needleand a production process of an ink-receiving layer making use of thesol. The shape of the alumina hydrate and the solids concentration of adispersion are also described. On the contrary, the present inventor hasfound the use of non-crystal alumina hydrates in the form of "a flatplate".

As described above, such a non-crystal alumina hydrate in the form of aflat plate is produced by hydrolyzing an aluminum long-chain alkoxide.Therefore, it is possible to obtain an alumina hydrate containing littleion and raw alcohol with ease. According to this hydrolysis, the shapecontrol for forming particles of the alumina hydrate into the flat platecan be made with ease. The non-crystal alumina hydrate in the flat plateform has higher dispersibility than the known alumina hydrate in theneedle form. Further, the resulting alumina hydrate is dried once topowder without directly preparing a dispersion in a sol state, and thenused, whereby a dispersion high in solids concentration and low inviscosity can be prepared with ease.

4) The prior art discloses an alumina hydrate of a pseudoboehmitestructure. It is also disclosed to add additives such as silica, boria,titania and magnesia to the alumina hydrate. On-the contrary, thepresent inventor has found that an alumina hydrate containing titaniumdioxide has an improving effect on both adsorption of a dye in an inkand dispersibility.

The titanium dioxide-containing alumina hydrate is better indye-adsorbing ability than alumina hydrate containing no titaniumdioxide because the dye is adsorbed on the strongly electron-acceptableAl³⁺ formed by the action of titanium dioxide, or the titanium ion oftitanium dioxide forms a coordinate bond with the dye. FIGS. 9A and 9Bschematically illustrate exposed states of titanium dioxide in pores inthe respective cases where titanium dioxide is internally contained inthe alumina hydrate and where titanium dioxide is added (mixed) to thealumina hydrate. In the mixed system, the titanium dioxide is partlyexposed in the pore. In the contained system, the titanium dioxide isentirely exposed in the pore. If the titanium dioxide is present in thesame proportion, the system according to the present invention isgreater on the amount of titanium dioxide exposed.

In the titanium dioxide-containing alumina hydrate used in the presentinvention, the titanium dioxide exists in the close vicinity of thesurface of the alumina hydrate in the form of such ultrafine particlesthat they cannot be observed even through an electron microscope.Therefore, the surface area of the titanium dioxide in the interior ofthe pore is considerably great, and an adsorption site hence becomes fargreater than the mixed system, whereby the adsorptiveness of a dye in anink to the alumina hydrate is exhibited to a significant extent.

In the alumina hydrate mixed with titanium dioxide, its surface chargetends to be lost because the surface charges of the alumina hydrate andtitanium dioxide are opposite to each other, and hence neutralized.Therefore, the zeta-potential of its dispersion is low, and so thedispersion tends to aggregate. On the contrary, in the titaniumdioxide-containing alumina hydrate used in the present invention, thetitanium dioxide exists in the close vicinity of the surface of thealumina hydrate in the form of the ultrafine particles, whereby thesurface area of the titanium dioxide in the interior of the pore isconsiderably great, and little influence is exerted on the structure ofthe alumina hydrate. It also has an effect of lessening the reduction insurface charge of the alumina hydrate. Further, in the presentinvention, the titanium dioxide exists only in the vicinity of thesurface of the alumina hydrate. Therefore, the bulk properties of theinterior of the alumina hydrate are easy to be kept, which has an effectof exerting little influence on the surface charge.

The prior art describes a psuedoboehmite sol and a production process ofan ink-receiving layer making use of the sol. On the contrary, thenon-crystal titanium dioxide-containing alumina hydrates in the form ofa flat plate according to the present invention is produced byhydrolyzing, preferably, an aluminum long-chain alkoxide and titaniumalkoxide. Therefore, it is possible to obtain an alumina hydratecontaining little ion and raw alcohol with ease. According to thisprocess, the alumina hydrate tend to become particles in the form of aflat plate, and shape control can be made with ease. Further, titaniumdioxide exists in the close vicinity of the surfaces of the particles,so that the alumina hydrate has far higher dispersibility than the knownalumina hydrate in the needle form. Furthermore, the resulting titaniumdioxide-containing alumina hydrate is dried once to powder withoutdirectly preparing a dispersion (in particular, a dispersion forcoating) in a sol state, and then used, whereby a dispersion high insolids concentration and low in viscosity can be prepared with ease.

In each of the recording media according to the present invention, abinder capable of using in combination with the alumina hydrate may befreely selected from water-soluble polymers. For example, preference maybe given to polyvinyl alcohol or modified products thereof (cationicallymodified, anionically modified, silanol modified), starch or modifiedproducts thereof (oxidized, etherified), casein or modified productsthereof, gum arabic, cellulose derivatives such as carboxymethylcellulose, hydroxyethyl cellulose and hydroxypropyl cellulose,conjugated diene copolymer latexes such as SBR latexes, NBR latexes andmethyl methacrylate-butadiene copolymers, functional group-modifiedpolymer latexes, vinyl copolymer latexes such as ethylene-vinyl acetatecopolymers, polyvinyl pyrrolidone, maleic anhydride polymer orcopolymers thereof, acrylic ester copolymers, and the like. Thesebinders may be used either singly or in any combination thereof. Themixing ratio of the alumina hydrate to the binder may be optionallyselected from a range of from 1:1 to 30:1, preferably from 5:1 to 25:1.If the amount of the binder is less than the lower limit of the aboverange, the mechanical strength of the resulting ink-receiving layer isinsufficient, which forms the cause of cracking and dusting. If theamount is greater than the upper limit of the above range, the porevolume of the resulting ink-receiving layer is reduced, resulting in arecording medium poor in ink absorptiveness.

The alumina hydrate and binder may optionally contain dispersants forthe alumina hydrate, viscosity modifiers, pH adjustors, lubricants,flowability modifiers, surfactants, antifoaming agents, water-proofings,foam suppressors, releasing agents, foaming agents, penetrants, coloringdyes, optical whitening agents, ultraviolet absorbents, antioxidants,antiseptics and mildewproofing agents.

The water-proofings may be freely selected for use from the knownsubstances such as quaternary ammonium halides and quaternary ammoniumsalt polymers.

As the base material constituting the recording medium of the presentinvention, may be used paper webs such as suitably sized paper, waterleaf paper and resin-coated paper making use of polyethylene or thelike, sheet-like substance such as thermoplastic films, and cloths. Noparticular limitation is imposed on the base material. In the case ofthe thermoplastic films, may be used transparent films such as films ofpolyester, polystyrene, polyvinyl chloride, polymethyl methacrylate,cellulose acetate, polyethylene and polycarbonate, as well as opaquesheets opacified by the filling of an alumina hydrate or the formationof minute foams.

A dispersion of the alumina hydrate, which is suitably used in theproduction of the recording medium according to the present invention,can be prepared in the following manner. The above-described powderyalumina hydrate is added to deionized water to prepare a dispersioncontaining solids at a desired concentration. Mechanical shear force orultrasonic energy is applied to the dispersion, as needed, to controlthe particle size of the alumina hydrate. Thereafter, a binderdispersion separately prepared is added to the former dispersion. Theresulting mixture is subjected to dispersion, heating, defoaming and/orthe like as needed, thereby obtaining a final dispersion for coating.

In the recording media having an ink-receiving layer according to thepresent invention, as a process for forming the ink-receiving layer onthe base material, may be used a process in which the dispersioncontaining the alumina hydrate and the like is applied to the basematerial by means of a coater, and then dried. As a coating process, maybe used a generally-used coating technique making use of a blade coater,air knife coater, roll coater, brush coater, curtain coater, bar coater,gravure coater or sprayer. The coating weight of the dispersion iswithin a range of from 0.5 to 60 g/m², more preferably from 5 to 45 g/m²in dried state. As needed, the resulting recording medium may bysubjected to supercalendering or the like so as to improve thesmoothness of the ink-receiving layer.

The recording media of another type according to the present invention,in which the alumina hydrate is internally contained in the basematerial, can be produced using an internally-adding process in whichthe alumina hydrate (its dispersion) is added to a slurry containing afibrous material in a paper making process. In such an internally-addingprocess, a paper-strength improving agent, retention aid and colorantmay be added for use as needed. The retention aid may be selected fromcationic retention aids such as cationic starch anddicyanediamide-formalin condensates, and anionic retention aids such asanionic polyacrylamide and anionic colloidal silica. These may also beused in combination with each other.

Inks used in conducting recording on the recording media according tothe present invention comprises principally a coloring material (dye orpigment), a water-soluble organic solvent and water. Preferred examplesof the coloring material include water-soluble dyes represented bydirect dyes, acid dyes, basic dyes, reactive dyes and food colors.However, any coloring materials may be used so far as they provideimages satisfying required performance such as fixing ability, coloringability, brightness, stability, light fastness and the like incombination with the above-described recording media.

The water-soluble dyes are generally used by dissolving them in water ora solvent composed of water and at least one organic solvent. As apreferable solvent component for these dyes, may be used a mixed solventcomposed of water and at least one of various water-soluble organicsolvents. It is however preferable to control the content of water in anink within a range of from 20 to 90% by weight, more preferably from 60to 90% by weight.

Examples of the water-soluble organic solvents include alkyl alcoholshaving 1 to 4 carbon atoms, such as methyl alcohol, ethyl alcohol,n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol,tert-butyl alcohol and isobutyl alcohol; amides such asdimethylformamide and dimethylacetamide; ketones and keto alcohols suchas acetone and diacetone alcohol; ethers such as tetrahydrofuran anddioxane; polyalkylene glycols such as polyethylene glycol andpolypropylene glycol; alkylene glycols the alkylene moiety of which has2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, hexyleneglycol and diethylene glycol; thiodiglycol; 1,2,6-hexanetriol; glycerol;lower alkyl ethers of polyhydric alcohols, such as ethylene glycolmethyl ether, diethylene glycol methyl ether, diethylene glycol ethylether, triethylene glycol monomethyl ether and triethylene glycolmonoethyl ether; and the like. Among these many water-soluble organicsolvents, the polyhydric alcohols such as diethylene glycol, and thelower alkyl ethers of polyhydric alcohol, such as triethylene glycolmonomethyl ether and triethylene glycol monoethyl ether are preferred.The polyhydric alcohols are particularly preferred because they have aneffect as a lubricant for inhibiting the clogging of nozzles, which iscaused by the evaporation of water in an ink and hence the deposition ofa water-soluble dye.

A solubilizer may be added to the inks. Nitrogen-containing heterocyclicketones are typical solubilizers. Its object is to enhance thesolubility of the water-soluble dye in the solvent by leaps and bounds.For example, N-methyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone arepreferably used. In order to further improve the properties of inks, maybe added additives such as viscosity modifiers, surfactants, surfacetension modifiers, pH adjustors and specific resistance adjustors.

A preferred method of conducting recording by applying theabove-described ink to the recording medium is an ink-jet recordingmethod. As such a method, any systems may be used so far as they caneffectively eject an ink out of a nozzle to apply it to the recordingmedium. In particular, an ink-jet recording system described in JapanesePatent Application Laid-Open No. 54-59936, in which an ink undergoes arapid volumetric change by an action of thermal energy applied to theink, so that the ink is ejected out of a nozzle by the working forcegenerated by this change of state, may be used effectively.

EXAMPLES

The present invention will hereinafter be described more specifically bythe following Examples. However, the present invention is not limited tothese examples. The measurements of various properties according to thisinvention were conducted with the following points in mind:

1) BET Specific Surface Area, Pore Radius Distribution, Pore Volume andIsothermal Adsorption and Desorption Curve:

After an alumina hydrate sample or a recording medium sample in which anink-receiving layer had been formed on a PET film was thoroughly heatedand deaerated, measurement was conducted using the nitrogen adsorptionand desorption method (Autosorb 1, manufactured by Quanthachrome Co.).

i) The BET specific surface area was calculated in accordance with themethod of Brunauer, et al. J. Am. Chem. Soc., Vol. 60, 309 (1938)!.

ii) The pore radius and pore volume were calculated in accordance withthe method of Barrett, et al. J. Am. Chem. Soc., Vol. 73, 373 (1951)!.

iii) The relative pressure difference (ΔP) between adsorption anddesorption at 90 percent of the maximum amount of adsorbed gas was foundfrom an isothermal nitrogen adsorption and desorption curve.

2) X-ray Diffraction Pattern:

An X-ray diffractometer (manufactured by RIGAKU CORPORATION) was used.

3) Shape Observation of Alumina Hydrate (Aspect Ratio and SlendernessRatio):

An alumina hydrate sample was dispersed in deionized water, and theresultant dispersion was dropped on a collodion membrane to prepare asample for measurement. This sample was observed through a transmissiontype electron microscope (H-500, manufactured by Hitachi Ltd.).

4) Number of hydroxyl groups:

One gram of an alumina hydrate sample was weighed out to titrate it withtriethylaluminum.

5) Zeta-Potential:

An alumina hydrate sample was dispersed in deionized water to give asolids concentration of 0.1% by weight, and the dispersion was thenadjusted to pH 6 with a nitric acid, thereby conducting measurement.(Bi-ZETA plus, manufactured by Brookheaven Co., dispersion temperature:20° C., an acrylic cell was used.)

6) Solution Viscosity:

An aqueous dispersion sample at solids concentration of 15% by weight,20% by weight or 25% by weight was prepared to measure its viscosity at20° C. and a shear rate of 7.9 sec⁻¹ (in the case of the solidsconcentration of 15% by weight) or 10.9 sec⁻¹ (in the case of the solidsconcentration of 20% by weight or 25% by weight) by means of aVISCOMETER manufactured by TOKIMEC Co.

7) Nitrate Anion:

A nitrate anion was extracted from an alumina hydrate sample with hotwater to measure its quantity by an ion-exchange chromatograph (L-3720,manufactured by Hitachi Ltd.), thereby determining the quantity of thenitrate anion in terms of % by weight of dried alumina hydrate.

8) Quantitative Analysis of Titanium Dioxide:

The content of titanium dioxide in the whole alumina hydrate sample wasdetermined by fusing the alumina hydrate sample in a borate inaccordance with the ICP method (SPS 4000, manufactured bySeiko-Electronic Inc.). The distribution of titanium dioxide in thealumina hydrate sample was analyzed by means of an ESCA (Model 2803,manufactured by Surface Science Instruments Co.). The surface of thealumina hydrate sample was etched with an argon ion for 100 seconds and500 seconds to determine the change in content of the titanium dioxide.Etching conditions was as follows:

Argon pressure: 5×10⁻⁴ Pa

Voltage applied: 3 kV

Current (d.c.) applied: 3 mA.

FIRST ASPECT Examples 1 to 4

Aluminum dodeoxide was prepared in accordance with the process describedin U.S. Pat. No. 4,242,271. The aluminum dodeoxide was then hydrolyzedin accordance with the process described in U.S. Pat. No. 4,202,870 toprepare an alumina slurry. Water was added to the alumina slurry untilthe solid content of alumina hydrate was 7.9%. The pH of the aluminaslurry was 9.5. A 3.9% nitric acid solution was added to adjust the pHof the slurry. Colloidal sols were obtained under their correspondingaging conditions shown in Table 1. Each of these colloidal sols wasspray-dried at 75° C. to obtain its corresponding alumina hydrate. Thisalumina hydrate was non-crystal as shown by an X-ray diffraction patternin FIG. 2. As illustrated by a photograph (an electron microphotograph:60,000 magnifications) in FIG. 3, it was also in the form of a flatplate. The physical property values of the resulting alumina hydrateswere measured in accordance with the respective methods described above.The results are shown in Table 2 and FIGS. 5 and 6.

Polyvinyl alcohol (Gohsenol NH18, product of The Nippon SyntheticChemical Industry Co., Ltd.) was dissolved or dispersed in deionizedwater to obtain a 10% by weight solution or dispersion. The fourdifferent kinds of alumina hydrates obtained above were separatelysimilarly dispersed in deionized water to obtain 15% by weightdispersions. Each of the alumina hydrate dispersions and the polyvinylalcohol solution were weighed out to give a weight ratio of 10:1 interms of solids and mixed with each other. The resultant mixture wasstirred to obtain a mixed dispersion. The mixed dispersion was appliedby a die coating process to one side of a PET film (Lumiror, product ofToray Industries, Inc.) having a thickness of 100 μm to form anink-receiving layers having a thickness of 30 μm. FIG. 4 is a photograph(an electron microphotograph: 50,000 magnifications) illustrating thesection of the ink-receiving layer and indicates that the aluminahydrate in the form of a flat plate lies at random in the ink-receivinglayer. The physical property values of the ink-receiving layer weremeasured in accordance with the respective methods described above. Theresults are shown in Table 3. Printing was conducted on thethus-obtained recording media to evaluate their printability inaccordance with the following standards. The evaluation results are alsoshown in Table 3.

Printability:

Using an ink-jet printer equipped with four recording heads for yellow,magenta, cyan and black inks, each of said heads having 128 nozzles in aproportion of 16 nozzles per mm, ink-jet recording was conducted withinks of the following compositions, thereby evaluating the recordingmedia in ink-drying ability (absorptiveness), optical density of animage, bleeding and beading.

(1) Ink-Drying Ability:

After single-color or multi-color solid printing was conducted with theyellow, magenta, cyan and black inks of the following ink composition 1,the recorded area of each recording medium was touched with a finger todetermine the drying condition of the inks on the surface of therecording medium. The quantity of ink in the single-color printing wasdetermined as 100%. The ink-drying ability was ranked as A where none ofthe inks adhered to the finger in an ink quantity of 200%, B where noneof the inks adhered to the finger in an ink quantity of 100%, or C whereany ink adhered to the finger in an ink quantity of 100%.

(2) Optical Density:

Solid printing was conducted separately with the yellow, magenta, cyanand black inks of the following ink composition 1. The optical densityof each of the images formed was determined by means of a Macbethreflection densitometer RD-918.

(3) Bleeding and Beading:

After single-color or multi-color solid printing was conducted with theyellow, magenta, cyan and black inks of the following ink composition 1,the recording media were evaluated by whether bleeding occurred on theirsurfaces. Besides, single-color or multi-color solid printing wasconducted with the respective yellow, magenta, cyan and black inks ofthe following two ink compositions to visually evaluate the recordingmedia by whether beading occurred. The quantity of ink in thesingle-color printing was determined as 100%. The resistance to bleedingor the resistance to beading of the recording media was ranked as Awhere bleeding or beading did not occur in an ink quantity of 200%, Bwhere bleeding or beading did not occur in an ink quantity of 100%, or Cwhere bleeding or beading occurred in an ink quantity of 100%.

    ______________________________________    Ink composition 1:    Dye                 5 parts    Diethylene glycol  10 parts    Polyethylene glycol                       10 parts    Water              75 parts.    Ink composition 2:    Dye                 5 parts    Glycerol           15 parts    Polyethylene glycol                       20 parts    Water              70 parts.    Dye in ink:    Yellow (Y):        C.I. Direct Yellow 86    Magenta (M):       C.I. Acid Red 35    Cyan (C):          C.I. Direct Blue 199    Black (Bk):        C.I. Food Black 2.    ______________________________________

Examples 5 to 8

Each of the alumina hydrate dispersions prepared in Examples 1 to 4 andthe polyvinyl alcohol dispersion as described in Examples 1 to 4 wereweighed out to give a weight ratio of 15:1 in terms of solids and mixedwith each other. The resultant mixture was stirred to obtain a mixeddispersion. The mixed dispersion was applied by an air knife coatingprocess to one side of a wood free paper web (Shiraoi 157, product ofDaishowa Paper Manufacturing Co., Ltd.) at a rate of 20 g/m² to form anink-receiving layer. Printing was conducted on the thus-obtainedrecording media to evaluate their printability in accordance with theabove-described standards. The evaluation results are shown in Table 4.

Examples 9 to 12

A paper web having a basis weight of 70 g/m² was made by means of aTAPPI standard sheet former by using, as raw pulp, 80 parts of bleachedhardwood kraft pulp (LBKP) having a freeness (C.S.F.) of 370 ml and 20parts of bleached softwood kraft pulp (NBKP) having a freeness of 410ml, incorporating, as a filler, each of the alumina hydrates prepared inExamples 1 to 4 in a proportion of 35% by weight based on the solidcontent of the pulp and as a retention aid, cationic starch (CATOF,product of Oji National K.K.) in a proportion of 0.3% by weight based onthe solid content of the pulp into the pulp, and then adding 0.05% byweight of a polyacrylamide retention aid (Pearlflock FR-X, product ofSeiko Chemical Industries Co., Ltd.) right before paper making. A 2%solution of oxidized starch (MS3800, product of Nihon Shokuhin Kako Co.,Ltd.) was then applied to the web by a size press to obtain a recordingmedia. Printing was conducted on the thus-obtained recording media toevaluate their printability in accordance with the above-describedstandards. The evaluation results are shown in Table 5.

Comparative Example 1

An alumina sol (AS-2, product of Catalyst & Chemical Industries Co.,Ltd.) and polyvinyl alcohol (PVA 117, product of Kuraray Co., Ltd.) wereapplied to the same PET film as that used in Example 1 in accordancewith the process described in Example 1 of Japanese Patent ApplicationLaid-Open No. 4-4181 to prepare a recording medium. The zeta-potentialof the alumina sol was measured in accordance with the method describedabove. Further, the alumina sol was concentrated to a solidsconcentration of 15% to measure its viscosity. The physical propertyvalues and evaluation results thereof are shown in Table 6.

Comparative Example 2

A recording medium was prepared by using an alumina sol (AS-3, productof Catalyst & Chemical Industries Co., Ltd.) and the same polyvinylalcohol as that used in Comparative Example 1 in accordance with theprocess described in Example 4 of Japanese Patent Application Laid-OpenNo. 4-4181. The physical property values and evaluation results thereofare shown in Table 6.

Comparative Example 3

A recording medium was prepared by using an alumina sol (100, product ofNissan Chemical Industries, Ltd.) and the same polyvinyl alcohol as thatused in Comparative Example 1 in accordance with the process describedin Example 1 of Japanese Patent Application Laid-Open No. 3-143678. Thephysical property values and evaluation results thereof are shown inTable 6.

Comparative Example 4

An alumina sol was prepared in accordance with the process described inExample 1 of Japanese Patent Application Laid-Open No. 5-32037. Arecording medium was prepared by using this alumina sol and the samepolyvinyl alcohol as that used in Comparative Example 1. The physicalproperty values and evaluation results thereof are shown in Table 6.

                  TABLE 1    ______________________________________                  Sample    Aging condition                  Ex. 1  Ex. 2      Ex. 3                                         Ex. 4    ______________________________________    pH before aging                  5.6    6.9        6.0  5.8    Aging temperature                  110    150        180  120    (° C.)    Aging period (hrs)                  8      4          3    5    Aging apparatus                  Auto-  Auto-      Auto-                                         Auto-                  clave  clave      clave                                         clave    ______________________________________

                  TABLE 2    ______________________________________                 Sample    Item determined                 Ex. 1    Ex. 2    Ex. 3  Ex. 4    ______________________________________    Average particle                 43       38       32     26    size (nm)    Aspect ratio 3.3      5.6      7.9    10.0    Slenderness ratio                 0.7      0.7      0.7    0.7    BET specific 75       93       135    200    surface area (m.sup.2 /g)    Average pore radius                 125      85       50     30    (Å)    Half breadth (Å)                 100      80       50     20    Pore volume (cc/g)                 0.57     0.55     0.55   0.51    Relative pressure                 0.03     0.02     0.10   0.10    difference (ΔP)    Number of OH groups                 2.0 × 10.sup.20                          1.8 × 10.sup.20                                   1.5 × 10.sup.20                                          1.6 × 10.sup.20    (groups/g)    Zeta-potential (mV)                 20       23       17     17    Nitrate anion                 0.1      0.1      1.0    1.0    (% by weight)    Dispersion viscosity         15% by weight                     2.0      20     17     17    (cP) 26% by weight                     77       59     49     61         25% by weight                     409      460    430    457    ______________________________________

                  TABLE 3    ______________________________________                  Sample    Item determined                  Ex. 1   Ex. 2    Ex. 3  Ex. 4    ______________________________________    Average pore radius                  125     80       40     30    (Å)    Half breadth (Å)                  140     100      60     40    Pore volume    (cc/g)        0.53    0.50     0.50   0.49    (cc/m.sup.2)  9.0     8.6      8.4    8.2    Relative pressure                  0.03    0.07     0.02   0.10    difference (ΔP)    Printability:    Drying ability                  A       A        A      A    Optical density:    Y             1.58    1.55     1.53   1.53    M             1.47    1.50     1.48   1.52    C             1.60    1.57     1.61   1.55    Bk            1.64    1.61     1.59   1.57    Bleeding      A       A        A      A    Beading    Ink composition 1                  A       A        A      A    Ink composition 2                  A       A        A      A    ______________________________________

                  TABLE 4    ______________________________________                 Sample    Item determined                 Ex. 5     Ex. 6   Ex. 7                                        Ex. 8    ______________________________________    Printability:    Drying ability                 A      A          A    A    Optical density:    Y            1.42   1.42       1.44 1.43    M            1.43   1.47       1.46 1.45    C            1.47   1.45       1.46 1.49    Bk           1.48   1.47       1.45 1.46    Bleeding     A      A          A    A    Beading    Ink composition 1                 A      A          A    A    Ink composition 2                 A      A          A    A    ______________________________________

                  TABLE 5    ______________________________________                 Sample    Item determined                 Ex. 9   Ex. 10    Ex. 11                                         Ex. 12    ______________________________________    Printability:    Drying ability                 A       A         A     A    Optical density:    Y            1.02    1.02      1.04  1.03    M            1.03    1.07      1.06  1.05    C            1.07    1.05      1.06  1.09    Bk           1.08    1.07      1.05  1.06    Bleeding     A       A         A     A    Beading    Ink composition 1                 A       A         A     A    Ink composition 2                 A       A         A     A    ______________________________________

                  TABLE 6    ______________________________________                  Sample                  Comp.   Comp.     Comp. Comp.    Item determined                  Ex. 1   Ex. 2     Ex. 3 Ex. 4    ______________________________________    Zeta-potential (mV)                  10      7         9     10    Dispersion    200     250       180   230    viscosity (cP)    Average pore radius                  20      33        20    60    (Å)    Peak 1 of pore                  20      30        22    60    distribution (Å)    Peak 2 of pore                  --      --        --    --    distribution (Å)    Half breadth (Å)                  10      14        12    15    Pore volume    (cc/g)        0.83    0.50      0.06  0.66    (cc/m.sup.2)  1.0     0.8       0.01  2.0    Relative pressure                  0.25    0.25      0.23  0.23    difference (ΔP)    Printability:    Drying ability                  C       C         C     C    Optical density:    Y             1.68    1.67      1.66  1.69    M             1.51    1.54      1.53  1.50    C             1.50    1.52      1.51  1.53    Bk            1.46    1.48      1.47  1.46    Bleeding      B       B         B     A    Beading    Ink composition 1                  B       B         B     A    Ink composition 2                  C       B         C     B    ______________________________________

SECOND ASPECT Examples 13 to 16

Alumina hydrates were obtained in the same manner as in Examples 1 to 4except that the aging conditions in Examples 1 to 4 were changed toaging conditions shown in Table 7.

These alumina hydrates showed an X-ray diffraction pattern similar tothat illustrated in FIG. 2 and were hence amorphous. A photographsimilar to the photograph (an electron microphotograph: 60,000magnifications) in FIG. 3 was taken, and it was hence confirmed thatthey were in the form of a flat plate. The physical property values ofthe alumina hydrates were measured in accordance with the respectivemethods described above. The results are shown in Table 8 and FIGS. 7and 8.

                  TABLE 7    ______________________________________                  Sample    Aging condition                  Ex. 13  Ex. 14    Ex. 15                                          Ex. 16    ______________________________________    pH before aging                  6.6     6.9       7.0   6.8    Aging temperature                  30      45        50    50    (° C.)    Aging period  2 weeks 12 days   8 days                                          5 days    Aging apparatus                  Oven    Oven      Oven  Auto-                                          clave    ______________________________________

Recording media comprising a PET film and an ink-receiving layerprovided on the PET film were obtained in the same manner as in Examples1 to 4 except that these alumina hydrates were respectively used.

The physical property values of the ink-receiving layers of theserecording media and the evaluation results as to the printability ofthese recording media are shown in Table 9.

The evaluation of the printability was conducted in accordance with thefollowing standards.

Printability:

Using an ink-jet printer equipped with four recording heads for yellow,magenta, cyan and black inks, each of said heads having 128 nozzles in aproportion of 16 nozzles per mm, ink-jet recording was conducted withthe inks of the ink composition 1 described in Examples 1 to 4, therebyevaluating the recording media in ink-drying ability (absorptiveness),optical density of an image, bleeding and beading.

(1) Ink-Drying Ability:

After single-color or multi-color solid printing was conducted with theyellow, magenta, cyan and black inks, the recorded area of eachrecording medium was touched with a finger to determine the dryingcondition of the inks on the surface of the recording medium. Thequantity of ink in the single-color printing was determined as 100%. Theink-drying ability was ranked as AA where none of the inks adhered tothe finger in an ink quantity of 300%, A where none of the inks adheredto the finger in an ink quantity of 200%, B where none of the inksadhered to the finger in an ink quantity of 100%, or C where any inkadhered to the finger in an ink quantity of 100%.

(2) Optical Density:

Solid printing was conducted with the black ink. The optical density ofthe image formed was determined by means of a Macbeth reflectiondensitometer RD-918.

(3) Bleeding and Beading:

After single-color or multi-color solid printing was conducted with theyellow, magenta, cyan and black inks, the recording media were visuallyevaluated by whether bleeding or beading occurred on their surfaces. Thequantity of ink in the single-color printing was determined as 100%. Theresistance to bleeding or the resistance to beading of the recordingmedia was ranked as AA where bleeding or beading did not occur in an inkquantity of 300%, A where bleeding or beading did not occur in an inkquantity of 200%, B where bleeding or beading did not occur in an inkquantity of 100%, or C where bleeding or beading occurred in an inkquantity of 100%.

                  TABLE 8    ______________________________________                Sample    Item determined                Ex. 13   Ex. 14   Ex. 15 Ex. 16    ______________________________________    Average particle                40       35       31     28    size (nm)    Aspect ratio                3.8      5.8      7.6    9.8    Slenderness ratio                0.7      0.7      0.7    0.7    BET specific                80       95       130    190    surface area (m.sup.2 /g)    Peak 1 of pore                125      110      140    120    distribution (Å)    Peak 2 of pore                17       30       50     60    distribution (Å)    Pore volume (cc/g)                0.57     0.55     0.55   0.51    Volume ratio of                5        8        10     10    peak 2 (%)    Relative pressure                0.03     0.02     0.10   0.10    difference (ΔP)    Number of OH groups                1.9 × 10.sup.20                         1.5 × 10.sup.20                                  1.7 × 10.sup.20                                         2.0 × 10.sup.20    (groups/g)    Zeta-potential (mV)                20       23       17     17    Nitrate anion                0.1      0.5      0.7    1.0    (% by weight)    Dispersion viscosity         15% by weight                    18       18     17     16    (cP) 20% by weight                    43       50     80     75         25% by weight                    415      430    480    467    ______________________________________

                  TABLE 9    ______________________________________                 Sample    Item determined                 Ex. 13  Ex. 14    Ex. 15                                         Ex. 16    ______________________________________    Peak 1 of pore                 125     110       125   130    distribution (Å)    Peak 2 of pore                 25      30        40    60    distribution (Å)    Pore volume    (cc/g)       0.53    0.50      0.50  0.49    (cc/m.sup.2) 9.0     8.6       8.4   8.2    Relative pressure                 0.03    0.07      0.02  0.10    difference (ΔP)    Volume ratio of                 5       8         10    10    peak 2 (%)    Printability:    Drying ability                 AA      AA        AA    AA    Optical density                 1.65    1.67      1.66  1.67    Bleeding     AA      AA        AA    AA    Beading      AA      AA        AA    AA    ______________________________________

Examples 17 to 20

Each of the alumina hydrate dispersions prepared in Examples 13 to 16and the polyvinyl alcohol dispersion as described in Examples 1 to 4were weighed out to give a weight ratio of 15:1 in terms of solids andmixed with each other. The resultant mixture was stirred to obtain amixed dispersion. The mixed dispersion was applied by an air knifecoating process to one side of a wood free paper web (Shiraoi 157,product of Daishowa Paper Manufacturing Co., Ltd.) at a rate of 20 g/m²to form an ink-receiving layer. Printing was conducted on thethus-obtained recording media to evaluate their printability inaccordance with the above-described standards. The evaluation resultsare shown in Table 10.

                  TABLE 10    ______________________________________                 Sample    Item determined                 Ex. 17  Ex. 18    Ex. 19                                         Ex. 20    ______________________________________    Printability:    Drying ability                 AA      AA        AA    AA    Optical density                 1.51    1.52      1.51  1.52    Bleeding     AA      AA        AA    AA    Beading      AA      AA        AA    AA    ______________________________________

Examples 21 to 24

Recording media were obtained in the same manner as in Examples 9 to 12except that the alumina hydrates prepared in Examples 13 to 16 wererespectively used. Printing was conducted on the thus-obtained recordingmedia to evaluate their printability in accordance with theabove-described standards. The evaluation results are shown in Table 11.

                  TABLE 11    ______________________________________                 Sample    Item determined                 Ex. 21  Ex. 22    Ex. 23                                         Ex. 24    ______________________________________    Printability:    Drying ability                 AA      AA        AA    AA    Optical density                 1.08    1.09      1.08  1.09    Bleeding     AA      AA        AA    AA    Beading      AA      AA        AA    AA    ______________________________________

THIRD ASPECT Examples 25 and 26

Aluminum dodeoxide was prepared in accordance with the process describedin U.S. Pat. No. 4,242,271. Isopropyltitanium (product of KishidaChemical Co., Ltd.) was then mixed in an amount 5/1000 times of theweight of the aluminum dodeoxide. The resulting aluminum dodeoxidemixture was hydrolyzed in accordance with the process described in U.S.Pat. No. 4,202,870 to prepare a titanium dioxide-containing aluminaslurry. Water was added to the alumina slurry until the solid content ofalumina hydrate was 7.9%. The pH of the alumina slurry was 9.5. A 3.9%nitric acid solution was added to adjust the pH of the slurry. Colloidalsols were obtained under their corresponding aging conditions shown inTable 13. Each of these colloidal sols was spray-dried to obtain itscorresponding alumina hydrate. This alumina hydrate showed an X-raydiffraction pattern similar to that illustrated in FIG. 2 and was hencenon-crystal. A photograph similar to the photograph (an electronmicrophotograph: 60,000 magnifications) in FIG. 3 was taken, and it washence confirmed that its form was a flat plate form. The surface of thealumina hydrate was observed through an FE-TEM (HF 2000, manufactured byHitachi Ltd.) of 500,000 magnifications. As a result, no titaniumdioxide was observed. The physical property values of the aluminahydrates were measured in accordance with the respective methodsdescribed above. The results are shown in Table 14 and FIGS. 10 and 11.

On the other hand, the observation by ESCA revealed that the valence oftitanium is +4 from the value of bound energy. Since no splittingoccurred on 3p peak for titanium and 2p peak for aluminum, there was nointeraction between titanium and aluminum. Namely, titanium dioxidesolely existed without interacting between titanium and aluminum. Whenthe surface of the titanium dioxide-containing alumina hydrate wasetched, the amount of titanium was decreased to half in the etching timeof 100 seconds. No titanium was detected in the etching time of 500seconds. Therefore, it was confirmed that the titanium dioxide existsonly in the vicinity of the surface of the alumina hydrate.

Recording media were obtained in the same manner as in Examples 1 to 4except that the titanium dioxide-containing alumina hydrates wererespectively used. The physical property values of their ink-receivinglayers and evaluation results of the recording media are shown in Table15. The evaluation was conducted in accordance with the followingstandards:

Printability:

Using an ink-jet printer equipped with four recording heads for yellow,magenta, cyan and black inks, each of said heads having 128 nozzles in aproportion of 16 nozzles per mm, ink-jet recording was conducted withthe inks of the ink composition 1 described in Examples 1 to 4, therebyevaluating the recording media in ink-drying ability (absorptiveness),optical density of an image, bleeding and beading.

(1) Ink-Drying Ability:

After single-color or multi-color solid printing was conducted with theyellow, magenta, cyan and black inks, the recorded area of eachrecording medium was touched with a finger to determine the dryingcondition of the inks on the surface of the recording medium. Thequantity of ink in the single-color printing was determined as 100%. Theink-drying ability was ranked as A where none of the inks adhered to thefinger in an ink quantity of 200%, B where none of the inks adhered tothe finger in an ink quantity of 100%, or C where any ink adhered to thefinger in an ink quantity of 100%.

(2) Optical Density:

Solid printing was conducted with the black ink. The optical density ofthe image formed was determined by means of a Macbeth reflectiondensitometer RD-918.

(3) Bleeding and Beading:

After single-color or multi-color solid printing was conducted with theyellow, magenta, cyan and black inks, the recording media were visuallyevaluated by whether bleeding or beading occurred on their surfaces. Thequantity of ink in the single-color printing was determined as 100%. Theresistance to bleeding or the resistance to beading of the recordingmedia was ranked as A where bleeding or beading did not occur in an inkquantity of 200%, B where bleeding or beading did not occur in an inkquantity of 100%, or C where bleeding or beading occurred in an inkquantity of 100%.

Examples 27 and 28

Aluminum dodeoxide was prepared in the same manner as in Examples 25 and26. The aluminum dodeoxide was hydrolyzed in the same manner as inExamples 25 and 26 to prepare an alumina slurry. The aluminum dodeoxideand isopropyltitanium (product of Kishida Chemical Co., Ltd.) were mixedat a mixing ratio of 100:5 by weight. Using the alumina slurry as anucleus for crystal growth, the mixture was hydrolyzed in the samemanner as in Examples 25 and 26 to prepare a titanium dioxide-containingalumina hydrate slurry. Water was added to the alumina slurry until thesolid content of alumina hydrate was 7.9%. The pH of the alumina slurrywas 9.5. A 3.9% nitric acid solution was added to adjust the pH of theslurry. Colloidal sols were obtained under their corresponding agingconditions shown in Table 13. Each of these colloidal sols wasspray-dried at 75° C. to obtain its corresponding alumina hydrate. Aswith those obtained in Examples 25 and 26, the alumina hydrate wasnon-crystal and was in the form of a flat plate. The physical propertyvalues of the alumina hydrates were measured in accordance with therespective methods described above. The results are shown in Table 14.As with those obtained in Examples 25 and 26, the titanium dioxideexisted only in the vicinity of the surface of the alumina hydrate.

Recording media were obtained in the same manner as in Examples 1 to 4except that the titanium dioxide-containing alumina hydrates wererespectively used. The physical property values of their ink-receivinglayers and evaluation results of the recording media are shown in Table15. The evaluation was conducted in accordance with the same methods asthose used in Examples 25 and 26.

                  TABLE 13    ______________________________________                  Sample    Aging condition                  Ex. 25  Ex. 26    Ex. 27                                          Ex. 28    ______________________________________    pH before aging                  5.6     6.9       6.9   7.3    Aging temperature                  110     150       40    50    (° C.)    Aging period  8 hours 4 hours   4 weeks                                          3 weeks    Aging apparatus                  Auto-   Auto-     Oven  Oven                  clave   clave    ______________________________________

                  TABLE 14    ______________________________________                 Sample    Item determined                 Ex. 25   Ex. 26   Ex. 27 Ex. 28    ______________________________________    Titanium dioxide                 0.150    0.140    0.150  0.140    content    (ICP, % by weight)    Bound energy (eV)                 459      459      459    459    Titanium dioxide                 0.02     0.02     0.02   0.02    content    (ESCA, % by atom    number)    Titanium dioxide    content after    etching of the surface    100 seconds  0.01     0.01     0.01   0.01    500 seconds  0.00     0.00     0.00   0.00    Average particle                 45.0     35.0     40.0   30.0    size (nm)    Aspect ratio 3.5      8.3      3.5    8.1    Slenderness ratio                 0.7      0.7      0.7    0.7    BET specific 76       134      70     140    surface area (m.sup.2 /g)    Average pore radius                 130      80       70     60    (Å)    Half breadth (Å)                 100      60       20     20    Peak 1 of pore                 130      80       120    140    distribution (Å)    Peak 2 of pore                 --       --       40     50    distribution (Å)    Pore volume (cc/g)                 0.57     0.55     0.57   0.55    Volume ratio of                 --       --       5      10    peak 2 (%)    Relative pressure                 0.03     0.10     0.03   0.10    difference (ΔP)    Number of OH groups                 1.6 × 10.sup.20                          1.7 × 10.sup.20                                   1.9 × 10.sup.20                                          1.5 × 10.sup.20    (groups/g)    Zeta-potential (mV)                 20       17       20     17    Nitrate anion                 0.1      0.5      0.1    0.5    (% by weight)    Dispersion viscosity         15% by weight                     17       15     18     13    (cP) 20% by weight                     40       70     53     83         25% by weight                     420      458    445    460    ______________________________________

                  TABLE 15    ______________________________________                  Sample    Item determined                  Ex. 25  Ex. 26    Ex. 27                                          Ex. 28    ______________________________________    Average pore radius                  125     90        75    65    (Å)    Half breadth (Å)                  95      50        20    20    Peak 1 of pore                  130     80        140   150    distribution (Å)    Peak 2 of pore                  --      --        50    70    distribution (Å)    Volume ratio of                  --      --        5     10    peak 2 (%)    Pore volume    (cc/g)        0.53    0.50      0.53  0.50    (cc/m.sup.2)  9.0     8.4       9.0   8.4    Relative pressure                  0.03    0.02      0.03  0.02    difference (ΔP)    Printability:    Drying ability                  A       A         A     A    Optical density                  1.71    1.72      1.71  1.70    Bleeding      A       A         A     A    Beading       A       A         A     A    ______________________________________

Examples 29 to 32

Each of the alumina hydrate dispersions prepared in Examples 25 to 28and the polyvinyl alcohol dispersion as described in Example 25 wereweighed out to give a weight ratio of 15:1 in terms of solids and mixedwith each other. The resultant mixture was stirred to obtain a mixeddispersion. The mixed dispersion was applied by an air knife coatingprocess to one side of a wood free paper web (Shiraoi 157, product ofDaishowa Paper Manufacturing Co., Ltd.) at a rate of 20 g/m² to form anink-receiving layer. The evaluation results of the recording media areshown in Table 16. The evaluation was conducted in accordance with thesame methods as those used in Examples 25 to 28.

                  TABLE 16    ______________________________________                Sample    Item determined                Ex. 29  Ex. 30    Ex. 31                                        Ex. 32    ______________________________________    Printability:    Drying ability                A       A         A     A    Optical density                1.65    1.67      1.65  1.66    Bleeding    A       A         A     A    Beading     A       A         A     A    ______________________________________

Examples 33 to 36

Recording media were obtained in the same manner as in Examples 9 to 12except that the alumina hydrates prepared in Examples 25 to 28 wererespectively used. Printing was conducted on the thus-obtained recordingmedia to evaluate their printability in accordance with theabove-described standards. The evaluation results are shown in Table 17.

                  TABLE 17    ______________________________________                Sample    Item determined                Ex. 33  Ex. 34    Ex. 35                                        Ex. 36    ______________________________________    Printability:    Drying ability                A       A         A     A    Optical density                1.08    1.07      1.08  1.09    Bleeding    A       A         A     A    Beading     A       A         A     A    ______________________________________

The recording media according to the present invention and the ink-jetrecording method making use of these recording media have the followingadvantageous effects.

In the First Aspect:

1) Individual dyes and solvent components in inks were selectivelyadsorbed to pores having a specific radius. Therefore, when a mediumhaving wide pore radius distribution is used, printability becomes hardto be affected by the composition of ink. Accordingly, selectivity tothe composition of ink becomes higher.

2) Since the recording media have no hysteresis, the solvent componentin an ink is easy to be desorbed. Therefore, the ink-drying ability ofthe media is improved, and so bleeding and setoff can be prevented.

3) When alumina in the form of a flat plate is used, the spaces amongits particles can be widened if the losest packing is adopted.Therefore, there can be obtained a medium having pores considerably widein pore radius distribution.

4) Since the alumina hydrate has good dispersibility, the viscosity of adispersion can be kept low if the solids concentration of the dispersionis high.

5) Since the alumina hydrate has good dispersibility even at a neutralregion near pH 7, the amount of an acid added to the dispersion can bedecreased.

In the Second Aspect:

1) Since the individual pigments or ink-receiving layers have at leasttwo peaks in pore radius distribution, the function of the pores can bedivided.

2) Since a dye in an ink is effectively adsorbed to pores having arelatively small radius, images good in resolution and sufficient inoptical density can be provided.

3) Since a solvent component in the ink can be quickly absorbed in poreshaving a relatively large radius, images free of beading, bleeding andrunning of the ink and good in resolution can be provided.

4) Since the recording media have no hysteresis, the solvent componentin the ink is easy to be desorbed. Therefore, the ink-drying ability ofthe media is improved, and so bleeding and setoff can be prevented.

5) When alumina in the form of a flat plate is used, the spaces amongits particles can be widened if the closest packing is adopted.Therefore, there can be obtained a medium having pores considerably widein pore radius distribution.

5 6) Since the alumina hydrate has good dispersibility, the viscosity ofa dispersion can be kept low if the solids concentration of thedispersion is high.

7) Since the alumina hydrate has good dispersibility even at a neutralregion near pH 7, the amount of an acid added to the dispersion can bedecreased.

In the Third Aspect:

1) Both dye-adsorbing ability and dispersibility can be improved bycontaining titanium dioxide in the alumina hydrate. Since the viscosityof the dispersion can be kept low even if the solids concentration ofthe dispersion is high, the coating thickness of the ink-receiving layercan be thickened. Further, since the adsorption and fixing of an inkupon printing can be improved, changes with time can be prevented.

2) When alumina in the form of a flat plate is used, the spaces amongits particles can be widened if the closest packing is adopted.Therefore, there can be obtained a medium having pores considerably widein pore radius distribution.

3) Since the alumina hydrate has good dispersibility, the viscosity of adispersion can be kept low if the solids concentration of the dispersionis high.

4) Since the alumina hydrate has good dispersibility even at a neutralregion near pH 7, the amount of an acid added to the dispersion can bedecreased.

5) Since titanium dioxide is colorless, the ink-receiving layer is notcolored even when it is added.

6) Individual dyes and solvent components in inks were selectivelyadsorbed to pores having a specific radius. Therefore, when a mediumhaving wide pore radius distribution is used, printability becomes hardto be affected by the composition of ink. Accordingly, selectivity tothe composition of ink becomes higher.

7) Since the individual titanium dioxide-containing alumina hydrates orink-receiving layers have at least two peaks in pore radiusdistribution, the function of the pores can be divided. Since a dye inan ink is effectively adsorbed to pores having a relatively smallradius, images good in resolution and sufficient in optical density canbe provided. Since a solvent component in the ink can be quicklyabsorbed in pores having a relatively large radius, images free ofbeading, bleeding and running of the ink and good in resolution can beprovided.

8) Since the recording media have no hysteresis, the solvent componentin the ink is easy to be desorbed. Therefore, the ink-drying ability ofthe media is improved, and so bleeding and setoff can be prevented.

While the present invention has been described with respect to what ispresently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. To the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims. The scope of the following claims is to beaccorded to the broadest interpretation so as to encompass all suchmodifications and equivalent structures and functions.

What is claimed is:
 1. A recording medium comprising a substrate and anink-receiving layer containing an alumina hydrate and a binder providedon the substrate, wherein the alumina hydrate has at least two peaks inpore radius distribution, one of the peaks being located at a poreradius of smaller than 100 Å and the other being located at a poreradius within a range of from 100 to 200 Å.
 2. The recording mediumaccording to claim 1, wherein the pore volume of pores having the peakat a pore radius of smaller than 100 Å in the alumina hydrate is withina range of from 0.1 to 10% by volume based on the total pore volume. 3.The recording medium according to claim 1, wherein the pore volume ofthe alumina hydrate is within a range of from 0.4 to 0.6 cc/g.
 4. Therecording medium according to claims 1, wherein the relative pressuredifference (ΔP) between adsorption and desorption at 90 percent of themaximum amount of adsorbed gas as found from an isothermal nitrogenadsorption and desorption curve for the alumina hydrate is not largerthan 0.2.
 5. The recording medium according to claim 1, wherein said oneof the peaks is located at a pore radius of from 10 to 60 Å.
 6. Arecording medium comprising a substrate and an ink-receiving layercontaining alumina hydrate which has at least two peaks in pore radiusdistribution, and a binder provided on the substrate, wherein theink-receiving layer has at least two peaks in pore radius distribution,one of the peaks of the ink-receiving layer being located at a poreradius of smaller than 100 Å and the other of the peaks of theink-receiving layer being located at a pore radius within a range offrom 100 to 200 Å.
 7. The recording medium according to claim 6, whereinthe pore volume of pores having the peak at a pore radius of smallerthan 100 Å in the ink-receiving layer is within a range of from 0.1 to10% by volume based on the total pore volume.
 8. The recording methodaccording to claim 6, wherein the pore volume of the ink-receiving layeris within a range of from 0.4 to 0.6 cc/g.
 9. The recording mediumaccording to claim 6, wherein the total pore volume of the ink-receivinglayer is at least 8 cc/m².
 10. The recording medium according to claim6, wherein the relative pressure difference (ΔP) between absorption anddesorption at 90 percent of the maximum amount of adsorbed gas as foundfrom an isothermal nitrogen adsorption and desorption curve for theink-receiving layer is not larger than 0.2.
 11. The recording mediumaccording to claim 6, wherein said one of the peaks of the ink-receivinglayer is located at a pore radius of from 10 to 60 Å.
 12. The recordingmedium according to claim 1 or 6, wherein the alumina hydrate isnon-crystalline.
 13. The recording medium according to claim 12, whereinthe alumina hydrate is in the form of a flat plate having an averageaspect ratio of 3 to
 10. 14. The recording medium according to claim 13,wherein the alumina hydrate has a BET specific surface area of 70 to 300m² /g.
 15. The recording medium according to claim 13, wherein thealumina hydrate has an average slenderness ratio of 0.6 to 1.0.
 16. Therecording medium according to claim 1 or 6, wherein the number ofhydroxyl groups in the alumina hydrate is at least 10²⁰ groups/g. 17.The recording medium according to claim 1 or 6, wherein the aluminahydrate has a zeta-potential of at least 15 mV at pH
 6. 18. Therecording medium according to claim 1 or 6, wherein the alumina hydrateis represented by the following formula:

    Al.sub.2 O.sub.3-n (OH).sub.2n.mH.sub.2 O

wherein n is an integer of 0 to 3, m is a number of 0 to 10, and n and mare not both zero.
 19. The recording medium according to claim 1 or 6,wherein the binder comprises a water-soluble polymer.
 20. The recordingmedium according to claim 1 or 6, wherein a mixing weight ratio of thealumina hydrate to the binder is in the range of from 1:1 to 30:1. 21.The recording medium according to claim 20, wherein the mixing weightratio of the alumina hydrate to the binder is in the range of from 5:1to 25:1.
 22. The recording medium according to claim 1 or 6, wherein thecoating weight of the ink-receiving layer is in the range of from 0.5 to60 g/m² in a dry state.
 23. The recording medium according to claim 22,wherein the coating weight of the ink-receiving layer is in the range offrom 5 to 45 g/m² in a dry state.